Optical storage systems are used in a wide range of applications. Such optical storage systems employ optical media (i.e., CDs, DVD discs, Blue Ray discs, HD discs, and other media) that stores data along tracks disposed radially about the disc-shaped media. The data may be in the form of reflective pits disposed in the media. The reflective pits are detected/written by optical read/write components that are moved radially to different tracks of the storage media.
Differential phase detection may be used during the reading of data from optical storage media. The differential phase detection generates a radial error signal that drives a radial control loop to properly align the optical read components with the track that is to be read. The differential phase detection signal may also be used when moving to a new radial location on the storage media (i.e., seeking). During such an operation, the differential phase detection signal may be post processed, along with other information, by a circuit known as a track counter. The track counter facilitates monitoring of the gross radial position of the optical read components.
A differential phase detector may use a photodetector array to determine whether the optical read components are aligned with the desired track. The photodetector array is used to measure a time-varying diffraction pattern. The physical dimensions of the features on the disc are comparable to the wavelength of the light used to read the data, and the photodetector array that processes the light reflected from the disc is illuminated by a diffraction pattern. The characteristics of this diffraction pattern are influenced by the radial position, and by the particular pattern of recorded data. When an objective lens of the optical read components is in alignment with a track centerline, the electrical signals generated by the elements of the photodetector are in phase. When there is a radial position error, however, the diffraction pattern rotates about the optical axis as a particular data bit is scanned.
The electrical signals provided by the photodetector array are communicated to a signal processing circuit. The signal processing circuit may include a phase detector that compares the phase relationship of the electrical signals. The phase relationship is used to generate the track error signal.
As the data density of optical media storage increases, detection of electrical signals from the photodetectors becomes more difficult. As a result, detection circuits for such high-density media may become more complicated and costly to implement. Further, phase detectors used in the signal processing circuitry may be subject to noise signals that inhibit the proper detection of the phase relationship of the electrical signals. This may result in corresponding errors in the radial error signal.